Electronegativity

 Electronegativity is the capasity of an atom attracting electron to itself.

Electronegativity of an atom is depends on its atomic radius. The increased atomic radius indicates its lower attraction to electron. Hence, lower the electronegativity. 

Atom of right side of same period of periodic table indicates its lower radius due to increased electron and proton number. Hence, shows gradual increase in electronegativity.